1. Field of the Invention
The present invention relates to a novel naphthoquinone derivative, and an electrophotosensitive material using the same.
2. Description of the Prior Art
In image forming apparatuses such as electrostatic copying machines, laser printers and facsimile devices for normal papers, there is widely used an electrophotosensitive material, especially so-called as an organic photosensitive material, comprising a conductive substrate and a photosensitive layer containing an electric charge generating material which generates an electric charge due to light irradiation, an electric charge transferring material which transfers the electric charge generated and a binding resin in which these substances are dispersed, the photosensitive layer being provided on the conductive substrate.
The organic photosensitive material is classified roughly into a single-layer photosensitive material wherein an electric charge generating material and an electric charge transferring material are contained in the same layer and a multi-layer photosensitive material comprising an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, which are mutually laminated. Among these, the multi-layer photosensitive material is conventionally employed. In a conventional normal multi-layer photosensitive material, an electric charge generating layer and an electric charge transferring layer having a film thickness larger than that of the electric charge generating layer are generally provided on the surface of a conductive layer in this order in view of a mechanical strength.
The electric charge transferring material include hole transferring material and electron transferring material. Among electric charge transferring materials which are known at present, almost all of electric charge transferring materials having a high carrier mobility are hole transferring materials. Therefore, when the photosensitive material, which is put into practical use, is the multi-layer photosensitive material wherein the electric charge transferring material is provided on the surface side, it becomes a negative charging type photosensitive material.
However, it is necessary that the negative charging type multi-layer photosensitive material is charged by negative-polarity corona discharge which generates large amount of ozone. Thus, there are problems such as influence of ozone on environment and deterioration of photosensitive material itself.
In order to solve these problems, an electron transferring material having a high carrier mobility has been developed and studied. In Japanese Laid-Open Patent Publication No. 1-206349, there is suggested that a compound having a diphenoquinone structure is used as the electron transferring material.
However, diphenoquinones are generally inferior in compatibility with a binding resin and are not uniformly dispersed in the binding resin so that a hopping distance of electrons becomes large and transfer of electrons in the low electric field does not easily arise. Therefore, diphenoquinones themselves have a high carrier mobility. However, when using them for the photosensitive material as the electron transferring material, characteristics thereof are not sufficiently developed and a residual potential of the photosensitive material becomes high, which results in insufficient photosensitivity.
As described above, almost all of organic photosensitive materials, which are put into practical use, are multi-layer photosensitive materials. However, the single-layer photosensitive material has a lot of advantages that it has a simple structure, can be easily produced in comparison with the multi-layer photosensitive material, and can inhibit formation of membrane defects to improve optical characteristics. Besides, when using the electron transferring material and hole transferring material in combination as the electric charge transferring material, one single-layer photosensitive material can be used for both positive and negative charging type photosensitive materials, thereby widening the application range of the photosensitive material. However, the above diphenoquinones have a problem that transferring of electrons and holes are inhibited by an interaction between the diphenoquinones and hole transferring material. Therefore, such a single-layer photosensitive material has never been put into practical use at present.